linux-kernel - Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata

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Date:   Thu, 25 May 2017 11:00:59 +0000
From:   Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:     "noamca@...lanox.com" <noamca@...lanox.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
Subject: Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata

Hi Noam,

On Thu, 2017-05-25 at 05:34 +0300, Noam Camus wrote:
> From: Noam Camus <noamca@...lanox.com>
> 
> Due to a HW bug in NPS400 we get from time to time false TLB miss.
> Workaround this by validating each miss.
> 
> Signed-off-by: Noam Camus <noamca@...lanox.com>
> ---
>  arch/arc/mm/tlbex.S |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
> index b30e4e3..1d48723 100644
> --- a/arch/arc/mm/tlbex.S
> +++ b/arch/arc/mm/tlbex.S
> @@ -274,6 +274,13 @@ ex_saved_reg1:
>  .macro COMMIT_ENTRY_TO_MMU
>  #if (CONFIG_ARC_MMU_VER < 4)
>  
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +	/* verify if entry for this vaddr+ASID already exists */
> +	sr    TLBProbe, [ARC_REG_TLBCOMMAND]
> +	lr    r0, [ARC_REG_TLBINDEX]
> +	bbit0 r0, 31, 88f
> +#endif

That's funny. I think we used to have something like that in the past.


>  	/* Get free TLB slot: Set = computed from vaddr, way = random */
>  	sr  TLBGetIndex, [ARC_REG_TLBCOMMAND]
>  
> @@ -287,6 +294,9 @@ ex_saved_reg1:
>  #else
>  	sr TLBInsertEntry, [ARC_REG_TLBCOMMAND]
>  #endif
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +88:
> +#endif

Not sure if label itself required wrapping in ifdefs. It just makes code bulkier
and harder to read.

-Alexey